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<div class="section abstract"><div class="htmlview paragraph">With the rising popularity of dual-fuel combustion, liquefied petroleum gas (LPG) can be utilized in high-compression diesel engines. Through production from biomass (biomass to liquid, BtL), biopropane as a direct substitute for LPG can contribute to a reduction in greenhouse gas emissions caused by combustion engines. In a conventional dual-fuel engine, the low reactivity fuel (LRF) propane is premixed with the intake air to form a homogeneous mixture. This air-fuel mixture is then ignited by the high reactivity fuel (HRF) in the form of a diesel pilot injection inside the cylinder. In the presented work, this premixed charge operation (PCO) is compared to a method where propane and diesel are blended directly upstream of the high-pressure pump (premixed fuel operation, PFO) in variable mixing ratios for different engine loads and speeds. Furthermore, the effects of internal and external exhaust gas recirculation are investigated for each operating mode. The results show that PCO allows higher propane ratios of up to 75 % at low loads, while PFO enables higher percentages of propane at medium and high loads (up to 50 %), allowing for a “reactivity on demand” approach. In addition, PFO shows significantly lower emissions of unburned hydrocarbons (-98.3 %) and carbon monoxide (-94.6 %) compared to PCO while soot emissions are reduced in both cases. The use of EGR allows nitrogen oxide emissions to be lowered to similar levels for both operation modes and shows benefits concerning unburned hydrocarbon (-73.5 %) and carbon monoxide (-62.9 %) emissions in PCO.</div></div>
<div class="section abstract"><div class="htmlview paragraph">With the rising popularity of dual-fuel combustion, liquefied petroleum gas (LPG) can be utilized in high-compression diesel engines. Through production from biomass (biomass to liquid, BtL), biopropane as a direct substitute for LPG can contribute to a reduction in greenhouse gas emissions caused by combustion engines. In a conventional dual-fuel engine, the low reactivity fuel (LRF) propane is premixed with the intake air to form a homogeneous mixture. This air-fuel mixture is then ignited by the high reactivity fuel (HRF) in the form of a diesel pilot injection inside the cylinder. In the presented work, this premixed charge operation (PCO) is compared to a method where propane and diesel are blended directly upstream of the high-pressure pump (premixed fuel operation, PFO) in variable mixing ratios for different engine loads and speeds. Furthermore, the effects of internal and external exhaust gas recirculation are investigated for each operating mode. The results show that PCO allows higher propane ratios of up to 75 % at low loads, while PFO enables higher percentages of propane at medium and high loads (up to 50 %), allowing for a “reactivity on demand” approach. In addition, PFO shows significantly lower emissions of unburned hydrocarbons (-98.3 %) and carbon monoxide (-94.6 %) compared to PCO while soot emissions are reduced in both cases. The use of EGR allows nitrogen oxide emissions to be lowered to similar levels for both operation modes and shows benefits concerning unburned hydrocarbon (-73.5 %) and carbon monoxide (-62.9 %) emissions in PCO.</div></div>
<div class="section abstract"><div class="htmlview paragraph">Dual-fuel engines powered by renewable fuels provide a potential solution for reducing the carbon footprint and emissions of transportation, contributing to the goal of achieving sustainable mobility. The investigation presented in the following uses a dual-fuel engine concept running on biogas (referred to as CNG in this paper) and the e-fuel polyoxymethylene dimethyl ether (OME). The current study focuses on the effects of exhaust gas rebreathing and external exhaust gas recirculation (EGR) on emissions and brake thermal efficiency (BTE).</div><div class="htmlview paragraph">A four-cylinder heavy-duty engine converted to dual-fuel operation was used to conduct the engine tests at a load point of 1600 min<sup>-1</sup> and 9.8 bar brake mean effective pressure (BMEP). The respective shares of high reactivity fuel (HRF, here: OME) and low reactivity fuel (LRF, here: CNG) were varied, as were the external and internal EGR rates and their combinations. CNG was injected into the intake manifold to create a homogeneous air-fuel mixture, while OME was introduced as a pilot injection directly into the combustion chamber. Results showed an increase in total hydrocarbons (THC) and carbon monoxide (CO) emissions, while nitric oxide (NOx) emissions were significantly reduced compared to diesel operation. Soot emissions were completely mitigated due to the absence of direct carbon bonds in both CNG and OME. For the initial stage of the study, exhaust gas rebreathing was implemented on only one exhaust valve through a second event lift. For the second part of the study, the second event lift was also installed on the other exhaust valve. At a substitution rate of 50 % CNG, THC emissions could be lowered by up to 35 %, CO emissions by up to 50 % and NOx emissions by up to 18 % with the use of internal EGR. The combination of internal and external EGR reduced emissions even further.</div></div>
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